Multi-photon reactive compositons with inorganic particles and method for fabricating structures

ABSTRACT

A multi-photon reactive composition including: (a) at least one reactive species; and (b) multi-photon photoinitiator system; and (c) a plurality of substantially inorganic particles, wherein the particles have an average particle size of less than about 10 microns in diameter.

TECHNICAL FIELD

[0001] This invention relates to multi-photon reactive compositions andmethods for fabricating structures that include inorganic particles witha multi-photon curing process.

BACKGROUND

[0002] Multi-photon induced photo-polymerization provides a means tofabricate three-dimensional devices with exquisite sub-micron resolutionin a single processing step. Multi-photon processes involve thesimultaneous absorption of two or more photons by an absorbingchromophore. The total energy of the absorbed photons equals the energyof a multi-photon absorption peak, even though each photon individuallyhas insufficient energy to excite the chromophore. Whereas single-photonabsorption scales linearly with the intensity of the incident radiation,two-photon absorption scales quadratically. Higher-order absorptionsscale with a related higher power of incident intensity. As a result, itis possible to perform multi-photon curing processes withthree-dimensional spatial resolution. Furthermore, the excitationradiation is not attenuated by single-photon absorption within areactive matrix or material, so it is possible to selectively excitemolecules at a greater depth within a material than would be possiblevia single-photon excitation.

[0003] Multi-photon fabrication can be used to manufacture mechanicaland optical devices, such as cantilevers, gears, shafts, andmicrolenses. Thus far, however, the technique has been limited toorganic polymers. There are many applications where the mechanical,electrical, thermal, and/or optical properties of conventional polymersystems can be inappropriate for the end device use. In other cases,suitable polymer systems can be available, but not easily amenable tophotoimaging. In certain applications, there is a need to enhance thephysical properties of the completed structures without significantlychanging the imaging mechanism.

SUMMARY

[0004] Addition of inorganic nanoparticles to the reactive compositionallows tailoring of the optical, thermal, mechanical, and dielectricproperties of the nanocomposite, while maintaining the speed, easyprocessing, and flexible chemistry provided by the organic components ofthe composition. Following exposure and development, the completedstructure can be left as is or can be pyrolyzed to remove the organiccomponents and leave a substantially inorganic structure. The longwavelength infrared light used for multi-photon imaging undergoesminimal scattering, and therefore, little loss of imaging resolution.

[0005] Resins with uniformly dispersed, non-aggregated particles can bephotopatterned in accordance with the method of the invention to achievehigh resolution features with little resolution loss due to scattering.The invention provides a method to manufacture three dimensionalinorganic structures without requiring any molding or embossing steps,circumventing the difficulties associated with the de-molding process ofstructures with micron size dimensions.

[0006] In one aspect, the invention relates to a multi-photon reactivecomposition including at least one reactive species, a multi-photonphotoinitiator system, and a plurality of substantially inorganicparticles, wherein the particles have an average particle size of lessthan about 10 microns in diameter. As used herein, the “diameter” refersnot only to the diameter of substantially spherical particles but alsoto the longest dimension of non-spherical particles.

[0007] In a second aspect, the invention relates to an article includingan at least partially reacted species, a multi-photon photoinitiatorsystem, and a plurality of substantially inorganic particles, whereinthe particles have an average particle size of less than about 10microns in diameter, and the particles are present in the composition atup to about 65% by volume.

[0008] In a third aspect, the invention provides a method for making anorganic-inorganic composite including:

[0009] (a) providing a multi-photon reactive composition including:

[0010] (1) a reactive species,

[0011] (2) a multi-photon photoinitiator system,

[0012] (3) and a plurality of substantially inorganic particles,

[0013] wherein the particles have an average particle size of less thanabout 10 microns in diameter; and

[0014] (b) irradiating the multi-photon reactive composition withsufficient light to at least partially react the composition; and (c)removing a soluble portion of the multi-photon reactive composition fromthe resulting composite. As used herein, the term “sufficient light”means light of sufficient intensity and appropriate wavelength to effectmultiphoton absorption.

DESCRIPTION OF DRAWINGS

[0015]FIG. 1 is a schematic representation of a multi-photon curingapparatus.

[0016]FIGS. 2A and 2B are a schematic representation of a method ofpreparing a three dimensional lattice structure having undercuts.

[0017]FIG. 3A shows a top view of a magnetic actuator that can be madeusing the composition of the invention.

[0018]FIG. 3B shows a side view of a magnetic actuator that can be madeusing the composition of the invention.

[0019]FIG. 3C shows a side view of the magnetic actuator of FIG. 4Bunder the influence of a magnetic field.

[0020] Like reference symbols in the various drawings indicate likeelements.

DETAILED DESCRIPTION Exposure System and Conditions

[0021] Referring to FIG. 1, an optical system 10 for use in theinvention includes a light source 12, an optical element 14, and amoveable stage 16. The stage 16 is preferably moveable in threedimensions. A partially completed article 18 mounted on the stage 16includes a surface 20 and an optional surface feature 22. Amulti-photon-reactive composition 24 is applied on the surface 20 or inthe feature 22. The light 26 originating from the light source 12 isthen focused to a point P within the volume of the reactive composition24 to control the three-dimensional spatial distribution of lightintensity within the composition to at least partially react thecomposition 24.

[0022] Generally, light from a pulsed laser can be passed through afocusing optical train to focus the beam within the volume of thereactive composition 24. Using the stage 16, or by moving the lightsource 12 (for example, moving a laser beam using galvo-mirrors), thefocal point P can be scanned or translated in a three-dimensionalpattern that corresponds to a desired shape. The reacted or partiallyreacted portion of the reactive composition 24 then creates athree-dimensional structure of a desired shape.

[0023] The light source 12 in the system 10 can be any light source thatproduces sufficient intensity to effect multi-photon absorption.Suitable sources include, for example, femtosecond near-infraredtitanium sapphire oscillators (for example, those available fromCoherent under the trade designation MIRA OPTIMA 900-F) pumped by anargon ion laser (for example, those available from Coherent under thetrade designation INNOVA). This laser, operating at 76 MHz, has a pulsewidth of less than 200 femtoseconds, is tunable between 700 and 980 nm,and has average power up to 1.4 Watts (for example, a Spectra-Physics,Inc., (1335 Terra Bella Avenue, Mountain View, Calif. 94043 USA) “MaiTai” model, operated at a wavelength λ=800 nm, a repetition frequency of80 MHz, and a pulse width of about 100 femtoseconds (1×10⁻¹³ sec), witha power level up to 1 Watt).

[0024] However, in practice, any light source that provides sufficientintensity (to effect multi-photon absorption) at a wavelengthappropriate for the photosensitizer (used in the photoreactivecomposition) can be utilized. Such wavelengths can generally be in therange of about 300 to about 1500 nm; preferably, from about 600 to about1100 nm; more preferably, from about 750 to about 850 nm. Peakintensities can generally be from about 10⁶ W/cm². The upper limit onpulse fluence is generally dictated by the ablation threshold of thephotoreactive composition. For example, Q-switched Nd:YAG lasers (forexample, those available from Spectra-Physics under the tradedesignation QUANTA-RAY PRO), visible wavelength dye lasers (for example,those available from Spectra-Physics under the trade designation SIRAHpumped by a Spectra-Physics Quanta-Ray PRO), and Q-switched diode pumpedlasers (for example, those available from Spectra-Physics under thetrade designation FCBAR) can also be utilized. Preferred light sourcesare near infrared pulsed lasers having a pulse length less than about10⁻⁸ second (more preferably, less than about 10⁻⁹ second; mostpreferably, less than about 10⁻¹¹ second). Other pulse lengths can beused as long as the peak intensity and ablation threshold criteria aboveare met. Continuous wave lasers can also be utilized.

[0025] Optical elements 14 useful in the system 10 include, for example,refractive optical elements (for example, lenses), reflective opticalelements (for example, retroreflectors or focusing mirrors), diffractiveoptical elements (for example, gratings, phase masks, and holograms),polarizing optical elements (for example, linear polarizers andwaveplates), diffusers, Pockels cells, waveguides, and the like. Suchoptical elements are useful for focusing, beam delivery, beam/modeshaping, pulse shaping, and pulse timing. Generally, combinations ofoptical elements can be utilized, and other appropriate combinationswill be recognized by those skilled in the art. It is often desirable touse optics with large numerical aperture (NA) to provide highly-focusedlight. However, any combination of optical elements that provides adesired intensity profile (and spatial placement thereof) can beutilized. For example, the exposure system can include a scanningconfocal microscope (for example, those available from BioRad under thetrade designation MRC600) equipped with a 0.75 NA objective (such as,for example, those available from Zeiss under the trade designation 20XFLUAR).

[0026] Exposure times generally depend upon the type of exposure systemused to cause image formation (and its accompanying variables such asnumerical aperture, geometry of light intensity spatial distribution,the peak light intensity during the laser pulse (higher intensity andshorter pulse duration roughly correspond to peak light intensity)), aswell as upon the nature of the multi-photon reactive compositionexposed. Generally, higher peak light intensity in the regions of focusallows shorter exposure times, everything else being equal. Linearimaging or “writing” speeds generally can be about 5 to 100,000microns/second using a laser pulse duration of about 10⁻⁸ to 10⁻¹⁵second (preferably, about 10⁻¹¹ to 10⁻¹⁴ second) and about 10² to 10⁹pulses per second (preferably, about 10³ to 10⁸ pulses per second).

[0027] The multi-photon reactive radiation 26 induces a reaction in thereactive composition that produces a material having solubilitycharacteristics different from those of the unexposed reactivecomposition. The resulting pattern of exposed and unexposed material canthen be developed by removing either the exposed or the unexposedregions with an appropriate solvent. An optional post exposure bakefollowing exposure but prior to development may be required forphotoreactive compositions containing epoxy type reactive species.Reacted, Complex, seamless three-dimensional structures can be preparedin this manner.

[0028] The resulting structures can have any suitable size and shape,but the method of the invention is particularly well suited for adding amicrostructure to a microstructured surface of an article. Thestructures can be formed on the surface of the article, or within or ona feature of the surface. Where such feature(s) exist on the surface ofan article, for example, continuous or discontinuous patterns ofdepressions, protrusions, posts, or channels, the structures can beformed in the feature(s). The feature(s) can be microscopic, where theterm “microscopic” refers to features of small enough dimension so as torequire an optic aid to the naked eye when viewed from any plane of viewto determine its shape. One criterion is found in Modern OpticEngineering by W. J. Smith, McGraw-Hill, 1966, pages 104-105 wherebyvisual acuity, “ . . . is defined and measured in terms of the angularsize of the smallest character that can be recognized.” Normal visualacuity is considered to be when the smallest recognizable lettersubtends an angular height of 5 minutes of arc on the retina. At typicalworking distance of 250 mm (10 inches), this yields a lateral dimensionof 0.36 mm (0.0145 inch) for this object. As used herein, the term“microstructure” means the configuration of features wherein at least 2dimensions of the features are microscopic.

[0029] Referring to FIG. 2A and FIG. 2B, a reactive composition 210 canbe applied to a substrate 212, such as a glass slide or silicon wafer.The substrate can optionally be treated with a primer (for example, asilane coupling agent) to enhance adhesion of the reactive compositionto the substrate. A lattice-like pattern 218 can be formed by exposingthe reactive composition 210 to form a series of layers 214 each havinga series of closely spaced bars 216, wherein the bars 216 of one layerare orthogonal to the bars 220 of the neighboring layer.

[0030] The photopatterned structure 218 is then pyrolyzed to preferablyremove substantially all the organic components (not shown in FIG. 2B).Typical pyrolysis conditions include heating the structure at 1° C./minto a temperature of between about 500° C. to about 900° C. and holdingat a temperature in that range for about 60 to about 240 minutes.

[0031] Following pyrolysis, the three-dimensional pyrolyzed structure issubstantially inorganic and partially sintered, with voids defined bythe size and shape of the particles. Preferably, the three-dimensionalstructure includes solid close packed spheres. In some applications, itcan be desirable to leave the structure partially porous (e.g., to allowflow of liquid through the pores). In other applications, the porousstructure can be sintered further to yield a fully consolidatedinorganic sintered structure.

[0032] Typical sintering conditions include heating the pyrolyzedstructure to a temperature of between about 900° C. to about 1400° C.and holding at a temperature in that range for about 2 hours to about 48hours. To aid in the consolidation process, the porous, pyrolyzedstructures can be doped with a variety of materials, such as metal saltsor other fluxing agents, such as, for example, boron oxide, boric acid,borax, and sodium phosphate. Alternatively, sol-gel precursors, such astetraethoxygermanium and tetraethoxysilane, can be imbibed into thepores to aid in reducing the porosity and/or adding functionality to thedevice (for example, increasing refractive index). Doping of theseporous structures with fluxing agents and/or sol-gel precursors followedby further sintering allows for the production of fully consolidatedinorganic structures. In addition, other materials such asorganometallic precursors can be added to the porous pyrolyzed structureto impart additional properties and/or function to the fabricateddevice.

[0033] After sintering, the structure has a substantially inorganiccomposition and dimensions that are smaller than prior to the sinteringstep. A narrow size distribution of particles sizes is also beneficialfor achieving uniform sintering.

[0034] Referring to FIGS. 3A and 3B, a curable embodiment of thecomposition can also be used to fabricate movable parts on a molded orphotopatterned article (e.g., a magnetic actuator) that can be movedusing an external energy source or an applied field (e.g., magnetic orelectric field). Referring to FIG. 3A and FIG. 3B, a molded orphotopatterned part 500 is shown having a body 505 and a flexibleextension region 512 that is connected to the part 500 by two flexibleprongs 518 and 520. A curable material 510 includes a plurality ofmagnetic particles 524 that have been oriented with their magnetizationdirections parallel to the prongs 518, 520. The curable material 510 isthen cured onto the flexible extension region 512 to yield a curedstructure 517 (FIG. 3B). A mirror 540 is attached to surface 525 of thecured material 517.

[0035] Referring to FIGS. 3B and 3C, an electromagnet 526 is situatedbelow the part 500. Upon activation of the electromagnet 526, themagnetic particles 524 within the cured material 517 respond to themagnetic field 522 generated by the electromagnet 526 to move theflexible extension region 512. The mirror 540 can be used to guide lightin a variety of directions depending on the orientation of the flexibleextension region 512.

Reactive Species

[0036] The multi-photon reactive compositions that can be used to formthe above-described structures include curable or non-curable reactivespecies, a multi-photon photoinitiator system, and a plurality ofsubstantially inorganic colloidal particles. The multi-photonphotoinitiator system includes a multi-photon photosensitizer, anelectron acceptor, and an optional electron donor.

[0037] Compositions of the invention can optionally further non-reactivespecies.

[0038] Curable species include addition-polymerizable monomers andoligomers and addition-crosslinkable polymers (such as free-radicallypolymerizable or crosslinkable ethylenically-unsaturated speciesincluding, for example, acrylates, methacrylates, and certain vinylcompounds such as styrenes), as well as cationically-polymerizablemonomers and oligomers and cationically-crosslinkable polymers(including, for example, epoxies, vinyl ethers, and cyanate esters), andthe like, and mixtures thereof.

[0039] Suitable ethylenically-unsaturated species are described, forexample, in U.S. Pat. No. 5,545,676, and include mono-, di-, andpoly-acrylates and methacrylates (for example, methyl acrylate, methylmethacrylate, ethyl acrylate, isopropyl methacrylate, n-hexyl acrylate,stearyl acrylate, allyl acrylate, glycerol diacrylate, glyceroltriacrylate, ethyleneglycol diacrylate, diethyleneglycol diacrylate,triethyleneglycol dimethacrylate, 1,3-propanediol diacrylate,1,3-propanediol dimethacrylate, trimethylolpropane triacrylate,1,2,4-butanetriol trimethacrylate, 1,4-cyclohexanediol diacrylate,pentaerythritol triacrylate, pentaerythritol tetraacrylate,pentaerythritol tetramethacrylate, sorbitol hexacrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane,tris-hydroxyethyl-isocyanurate trimethacrylate, the bis-acrylates andbis-methacrylates of polyethylene glycols of molecular weight about200-500, copolymerizable mixtures of acrylated monomers such as thosedescribed in U.S. Pat. No. 4,652,274, and acrylated oligomers such asthose described in U.S. Pat. No. 4,642,126); unsaturated amides (forexample, methylene bis-acrylamide, methylene bis-methacrylamide,1,6-hexamethylene bis-acrylamide, diethylene triamirie tris-acrylamideand beta-methacrylaminoethyl methacrylate); vinyl compounds (forexample, styrene, diallyl phthalate, divinyl succinate, divinyl adipate,and divinyl phthalate); and the like; and mixtures thereof.

[0040] Suitable curable polymers include polymers with pendant(meth)acrylate groups, for example, having from 1 to about 50(meth)acrylate groups per polymer chain. Examples of such polymersinclude aromatic acid (meth)acrylate half ester resins such as thoseavailable under the trade designation SARBOX from Sartomer (for example,SARBOX 400, 401, 402, 404, and 405). Other useful polymers curable byfree radical chemistry include those polymers that have a hydrocarbylbackbone and pendant peptide groups with free-radically polymerizablefunctionality attached thereto, such as those described in U.S. Pat. No.5,235,015. Mixtures of two or more monomers, oligomers, and/or reactivepolymers can be used if desired. Preferred ethylenically-unsaturatedspecies include acrylates, aromatic acid (meth)acrylate half esterresins, and polymers that have a hydrocarbyl backbone and pendantpeptide groups with free-radically polymerizable functionality attachedthereto.

[0041] Suitable cationically-curable species are described, for example,in U.S. Pat. Nos. 5,998,495 and 6,025,406 and include epoxy resins. Suchmaterials, broadly called epoxides, include monomeric epoxy compoundsand epoxides of the polymeric type and can be aliphatic, alicyclic,aromatic, or heterocyclic. These materials generally have, on theaverage, at least 1 polymerizable epoxy group per molecule (preferably,at least about 1.5 and, more preferably, at least about 2). Thepolymeric epoxides include linear polymers having terminal epoxy groups(for example, a diglycidyl ether of a polyoxyalkylene glycol), polymershaving skeletal oxirane units (for example, polybutadiene polyepoxide),and polymers having pendant epoxy groups (for example, a glycidylmethacrylate polymer or copolymer). The epoxides can be pure compoundsor can be mixtures of compounds containing one, two, or more epoxygroups per molecule. These epoxy-containing materials can vary greatlyin the nature of their backbone and substituent groups. For example, thebackbone can be of any type and substituent groups thereon can be anygroup that does not substantially interfere with cationic cure at roomtemperature. Illustrative of permissible substituent groups includehalogens, ester groups, ethers, sulfonate groups, siloxane groups, nitrogroups, phosphate groups, and the like. The molecular weight of theepoxy-containing materials can vary from about 58 to about 100,000 ormore.

[0042] Useful epoxy-containing materials include those which containcyclohexene oxide groups such as epoxycyclohexanecarboxylates, typifiedby 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate. A moredetailed list of useful epoxides of this nature is set forth in U.S.Pat. No. 3,117,099.

[0043] Other epoxy-containing materials that are useful include glycidylether monomers of the formula

[0044] where R′ is alkyl or aryl and n is an integer of 1 to 6. Examplesare glycidyl ethers of polyhydric phenols obtained by reacting apolyhydric phenol with an excess of a chlorohydrin such asepichlorohydrin (for example, the diglycidyl ether of2,2-bis-(2,3-epoxypropoxyphenol)-propane). Additional examples ofepoxides of this type are described in U.S. Pat. No. 3,018,262, and inHandbook of Epoxy Resins, Lee and Neville, McGraw-Hill Book Co., NewYork (1967).

[0045] Numerous commercially available epoxy resins can also beutilized. In particular, epoxides that are readily available includeoctadecylene oxide, epichlorohydrin, styrene oxide, vinyl cyclohexeneoxide, glycidol, glycidylmethacrylate, diglycidyl ethers of Bisphenol A(for example, those available under the trade designations EPON 828,EPON 825, EPON 1004, and EPON 1010 from Resolution Performance Products,formerly Shell Chemical Co., as well as those available under the tradedesignations DER 331, DER 332, and DER 334 from Dow Chemical Co.),vinylcyclohexene dioxide (for example, the compounds available under thetrade designations ERL 4206 from Union Carbide Corp.),3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexene carboxylate (for example,the compounds available under the trade designations ERL 4221, CyracureUVR 6110 or UVR 6105 from Union Carbide Corp.),3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methyl-cyclohexenecarboxylate (for example, the compounds available under the tradedesignation ERL 4201 from Union Carbide Corp.),bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate (for example, thecompounds available under the trade designation ERL 4289 from UnionCarbide Corp.), bis(2,3-epoxycyclopentyl) ether (for example, thecompounds available under the trade designation ERL 0400 from UnionCarbide Corp.), aliphatic epoxy modified from polypropylene glycol (forexample, those available under the trade designations ERL 4050 and ERL4052 from Union Carbide Corp.), dipentene dioxide (for example, thecompounds available under the trade designation ERL 4269 from UnionCarbide Corp.), epoxidized polybutadiene (for example, the compoundsavailable under the trade designations Oxiron 2001 from FMC Corp.),silicone resin containing epoxy functionality, flame retardant epoxyresins (for example, those available under the trade designation DER580, a brominated bisphenol type epoxy resin available from Dow ChemicalCo.), 1,4-butanediol diglycidyl ether of phenolformaldehyde novolak (forexample, those available under the trade designations DEN 431 and DEN438 from Dow Chemical Co.), resorcinol diglycidyl ether (for example,the compounds available under the trade designation KOPOXITE fromKoppers Company, Inc.), bis(3,4-epoxycyclohexyl)adipate (for example,those available under the trade designations ERL 4299 or UVR 6128, fromUnion Carbide Corp.), 2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-meta-dioxane (for example, the compounds available under thetrade designation ERL-4234 from Union Carbide Corp.), vinylcyclohexenemonoxide 1,2-epoxyhexadecane (for example, the compounds available underthe trade designation UVR-6216 from Union Carbide Corp.), alkyl glycidylethers such as alkyl C₈-C₁₀ glycidyl ether (for example, those availableunder the trade designation HELOXY MODIFIER 7 from ResolutionPerformance Products), alkyl C₁₂-C₁₄ glycidyl ether (for example, thoseavailable under the trade designation HELOXY MODIFIER 8 from ResolutionPerformance Products), butyl glycidyl ether (for example, thoseavailable under the trade designation HELOXY MODIFIER 61 from ResolutionPerformance Products), cresyl glycidyl ether (for example, HELOXYMODIFIER 62 from Resolution Performance Products), p-tert-butylphenylglycidyl ether (for example, Heloxy Modifier 65 from ResolutionPerformance Products), polyfunctional glycidyl ethers such as diglycidylether of 1,4-butanediol (for example, HELOXY MODIFIER 67 from ResolutionPerformance Products), diglycidyl ether of neopentyl glycol (forexample, HELOXY MODIFIER 68 from Resolution Performance Products),diglycidyl ether of cyclohexanedimethanol (for example, HELOXY MODIFIER107 from Resolution Performance Products), trimethylol ethanetriglycidyl ether (for example, HELOXY MODIFIER 44 from ResolutionPerformance Products), trimethylol propane triglycidyl ether (forexample, HELOXY MODIFIER 48 from Resolution Performance Products),polyglycidyl ether of an aliphatic polyol (for example, HELOXY MODIFIER84 from Resolution Performance Products), polyglycol diepoxide (forexample, HELOXY MODIFIER 32 from Resolution Performance Products),bisphenol F epoxides (for example, those available under the tradedesignations EPON 1138 from Resolution Performance Products or GY-281from Ciba-Geigy Corp.), and9,9-bis[4-(2,3-epoxypropoxy)-phenyl]fluorenone (for example, thoseavailable under the trade designation EPON 1079 from ResolutionPerformance Products).

[0046] Other useful epoxy resins comprise copolymers of acrylic acidesters of glycidol (such as glycidylacrylate and glycidylmethacrylate)with one or more copolymerizable vinyl compounds. Examples of suchcopolymers are 1:1 styrene-glycidylmethacrylate, 1:1methylmethacrylate-glycidylacrylate, and a 62.5:24:13.5methylmethacrylate-ethyl acrylate-glycidylmethacrylate. Other usefulepoxy resins are well known and contain such epoxides asepichlorohydrins, alkylene oxides (for example, propylene oxide),styrene oxide, alkenyl oxides (for example, butadiene oxide), andglycidyl esters (for example, ethyl glycidate).

[0047] Useful epoxy-functional polymers include epoxy-functionalsilicones such as those described in U.S. Pat. No. 4,279,717, which arecommercially available from the General Electric Company. These arepolydimethylsiloxanes in which 1-20 mole % of the silicon atoms havebeen substituted with epoxyalkyl groups (preferably, epoxycyclohexylethyl, as described in U.S. Pat. No. 5,753,346.

[0048] Blends of various epoxy-containing materials can also beutilized. Such blends can comprise two or more weight average molecularweight distributions of epoxy-containing compounds (such as lowmolecular weight (below 200), intermediate molecular weight (about 200to 10,000), and higher molecular weight (above about 10,000)).Alternatively or additionally, the epoxy resin can contain a blend ofepoxy-containing materials having different chemical natures (such asaliphatic and aromatic) or functionalities (such as polar andnon-polar). Other cationically-reactive polymers (such as vinyl ethersand the like) can additionally be incorporated, if desired.

[0049] Preferred epoxies include aromatic glycidyl epoxies (such as theEPON resins available from Resolution Performance Products) andcycloaliphatic epoxies (such as ERL 4221 and ERL 4299 available fromUnion Carbide).

[0050] Suitable cationically-curable species also include vinyl ethermonomers, oligomers, and reactive polymers (for example, methyl vinylether, ethyl vinyl ether, tert-butyl vinyl ether, isobutyl vinyl ether,triethyleneglycol divinyl ether (for example, those available under thetrade designation RAPI-CURE DVE-3 from International Specialty Products,Wayne, N.J.), trimethylolpropane trivinyl ether (for example, thoseavailable under the trade designation TMPTVE from BASF Corp., MountOlive, N.J.), and those available under the trade designation VECTOMERdivinyl ether resins from Allied Signal (for example, VECTOMER 2010,VECTOMER 2020, VECTOMER 4010, and VECTOMER 4020 and their equivalentsavailable from other manufacturers), and mixtures thereof. Blends (inany proportion) of one or more vinyl ether resins and/or one or moreepoxy resins can also be utilized. Polyhydroxy-functional materials(such as those described, for example, in U.S. Pat. No. 5,856,373(Kaisaki et al.)) can also be utilized in combination with epoxy- and/orvinyl ether-functional materials.

[0051] Non-curable reactive species include, for example, reactivepolymers whose solubility can be increased upon acid- or radical-inducedreaction. Such reactive polymers include, for example, aqueous insolublepolymers bearing ester groups that can be converted by photogeneratedacid to aqueous soluble acid groups (for example,poly(4-tert-butoxycarbonyloxystyrene). Non-curable reactive species alsoinclude the chemically-amplified photoresists described by R. D. Allen,G. M. Wallraff, W. D. Hinsberg, and L. L. Simpson in “High PerformanceAcrylic Polymers for Chemically Amplified Photoresist Applications,” J.Vac. Sci. Technol. B, 9, 3357 (1991). The chemically-amplifiedphotoresist concept is now widely used for microchip manufacturing,especially with sub-0.5 micron (or even sub-0.2 micron) features. Insuch photoresist systems, catalytic species (typically hydrogen ions)can be generated by irradiation, which induces a cascade of chemicalreactions. This cascade occurs when hydrogen ions initiate reactionsthat generate more hydrogen ions or other acidic species, therebyamplifying reaction rate. Examples of typical acid-catalyzedchemically-amplified photoresist systems include deprotection (forexample, t-butoxycarbonyloxystyrene resists as described in U.S. Pat.No. 4,491,628, tetrahydropyran (THP) methacrylate-based materials,THP-phenolic materials such as those described in U.S. Pat. No.3,779,778, t-butyl methacrylate-based materials such as those describedby R. D Allen et al. in Proc. SPIE 2438, 474 (1995), and the like);depolymerization (for example, polyphthalaldehyde-based materials); andrearrangement (for example, materials based on the pinacolrearrangements).

Multi-Photon Photoinitiator System (1) Multi-Photon Photosensitizers

[0052] Multi-photon photosensitizers suitable for use in themulti-photon reactive composition are capable of simultaneouslyabsorbing at least two photons when exposed to radiation from anappropriate light source in the exposure system. Preferred multi-photonphotosensitizers have a two-photon absorption cross-section greater thanthat of fluorescein (that is, greater than that of 3′,6′-dihydroxyspiro[isobenzofuran-1(3H), 9′-[9H]xanthen]3-one) when measuredat the same wavelength. Generally, the two photon absorptioncross-section can be greater than about 50×10⁻⁵⁰cm⁴sec/photon, asmeasured by the method described by C. Xu and W. W. Webb in J. Opt. Soc.Am. B, 13, 481 (1996) and WO 98/21521.

[0053] This method involves the comparison (under identical excitationintensity and photosensitizer concentration conditions) of thetwo-photon fluorescence intensity of the photosensitizer with that of areference compound. The reference compound can be selected to match asclosely as possible the spectral range covered by the photosensitizerabsorption and fluorescence. In one possible experimental set-up, anexcitation beam can be split into two arms, with 50% of the excitationintensity going to the photosensitizer and 50% to the referencecompound. The relative fluorescence intensity of the photosensitizerwith respect to the reference compound can then be measured using twophotomultiplier tubes or other calibrated detector. Finally, thefluorescence quantum efficiency of both compounds can be measured underone-photon excitation.

[0054] Methods of determining fluorescence and phosphorescence quantumyields are well-known in the art. Typically, the area under thefluorescence (or phosphorescence) spectrum of a compound of interest iscompared with the area under the fluorescence (or phosphorescence)spectrum of a standard luminescent compound having a known fluorescence(or phosphorescence) quantum yield, and appropriate corrections are made(which take into account, for example, the optical density of thecomposition at the excitation wavelength, the geometry of thefluorescence detection apparatus, the differences in the emissionwavelengths, and the response of the detector to different wavelengths).Standard methods are described, for example, by I. B. Berlman inHandbook of Fluorescence Spectra of Aromatic Molecules, Second Edition,pages 24-27, Academic Press, New York (1971); by J. N. Demas and G. A.Crosby in J. Phys. Chem. 75, 991-1024 (1971); and by J. V. Morris, M. A.Mahoney, and J. R. Huber in J. Phys. Chem. 80, 969-974 (1976).

[0055] Assuming that the emitting state is the same under one- andtwo-photon excitation (a common assumption), the two-photon absorptioncross-section of the photosensitizer, (δ_(sam)), is equal to δ_(ref) K(I_(sam)/I_(ref))(Φ_(sam)/Φ_(ref)), wherein δ_(ref) is the two-photonabsorption cross-section of the reference compound, I_(sam) is thefluorescence intensity of the photosensitizer, I_(ref) is thefluorescence intensity of the reference compound, Φ_(sam) is thefluorescence quantum efficiency of the photosensitizer, Φ_(ref) is thefluorescence quantum efficiency of the reference compound, and K is acorrection factor to account for slight differences in the optical pathand response of the two detectors. K can be determined by measuring theresponse with the same photosensitizer in both the sample and referencearms. To ensure a valid measurement, the clear quadratic dependence ofthe two-photon fluorescence intensity on excitation power can beconfirmed, and relatively low concentrations of both the photosensitizerand the reference compound can be utilized (to avoid fluorescencereabsorption and photosensitizer aggregration effects).

[0056] When the photosensitizer is not fluorescent, the yield ofelectronic excited states can be measured and compared with a knownstandard. In addition to the above-described method of determiningfluorescence yield, various methods of measuring excited state yield areknown (including, for example, transient absorbance, phosphorescenceyield, photoproduct formation or disappearance of photosensitizer (fromphotoreaction), and the like).

[0057] Preferably, the two-photon absorption cross-section of thephotosensitizer is greater than about 1.5 times that of fluorescein (or,alternatively, greater than about 75×10⁻⁵⁰ cm⁴sec/photon, as measured bythe above method); more preferably, greater than about twice that offluorescein (or, alternatively, greater than about 100×10⁻⁵⁰ cm⁴sec/photon); most preferably, greater than about three times that offluorescein (or, alternatively, greater than about 150×10⁻⁵⁰cm⁴sec/photon); and optimally, greater than about four times that offluorescein (or, alternatively, greater than about 200×10⁻⁵⁰ cm⁴sec/photon).

[0058] Preferably, the photosensitizer is soluble in the reactivespecies (if the reactive species is liquid) or is compatible with thereactive species and with any binders (as described below) that areincluded in the multi-photon reactive composition. Most preferably, thephotosensitizer is also capable of sensitizing2-methyl-4,6-bis(trichloromethyl)-s-triazine under continuousirradiation in a wavelength range that overlaps the single photonabsorption spectrum of the photosensitizer (single photon absorptionconditions), using the test procedure described in U.S. Pat. No.3,729,313. Using currently available materials, that test can be carriedout as follows:

[0059] A standard test solution can be prepared having the followingcomposition: 5.0 parts of a 5% (weight by volume) solution in methanolof 45,000-55,000 molecular weight, 9.0-13.0% hydroxyl content polyvinylbutyral (for example, those available under the trade designation BUTVARB76 from Monsanto); 0.3 parts trimethylolpropane trimethacrylate; and0.03 parts 2-methyl-4,6-bis(trichloromethyl)-s-triazine (see Bull. Chem.Soc. Japan, 42, 2924-2930 (1969)). To this solution can be added 0.01parts of the compound to be tested as a photosensitizer. The resultingsolution can then be knife-coated onto a 0.05 mm clear polyester filmusing a knife orifice of 0.05 mm, and the coating can be air dried forabout 30 minutes. A 0.05 mm clear polyester cover film can be carefullyplaced over the dried but soft and tacky coating with minimum entrapmentof air. The resulting sandwich construction can then be exposed forthree minutes to 161,000 Lux of incident light from a tungsten lightsource providing light in both the visible and ultraviolet range (suchas that produced from a FCH 650 W quartz-iodine lamp, available fromGeneral Electric). Exposure can be made through a stencil to provideexposed and unexposed areas in the construction. After exposure thecover film can be removed, and the coating can be treated with a finelydivided colored powder, such as a color toner powder of the typeconventionally used in xerography. If the tested compound is aphotosensitizer, the trimethylolpropane trimethacrylate monomer will bepolymerized in the light-exposed areas by the light-generated freeradicals from the 2-methyl-4,6-bis(trichloromethyl)-s-triazine. Sincethe polymerized areas will be essentially tack-free, the colored powderwill selectively adhere essentially only to the tacky, unexposed areasof the coating, providing a visual image corresponding to that in thestencil.

[0060] Preferably, a photosensitizer can also be selected based in partupon shelf stability considerations. Accordingly, selection of aparticular photosensitizer can depend to some extent upon the particularreactive species utilized (as well as upon the choices of electron donorcompound and/or electron acceptor).

[0061] Particularly preferred multi-photon photosensitizers includethose exhibiting large multi-photon absorption cross-sections, such asRhodamine B (that is,N-[9-(2-carboxyphenyl)-6-(diethylamino)-3H-xanthen-3-ylidene]-N-ethylethanaminiumchloride and the hexafluoroantimonate salt of Rhodamine B) and the fourclasses of photosensitizers described, for example, by Marder and Perryet al. WO 98/21521 and WO 99/53242. The four classes can be described asfollows: (a) molecules in which two donors are connected to a conjugatedπ-electron bridge; (b) molecules in which two donors are connected to aconjugated π-electron bridge which is substituted with one or moreelectron accepting groups; (c) molecules in which two acceptors areconnected to a conjugated π-electron bridge; and (d) molecules in whichtwo acceptors are connected to a conjugated π-electron bridge which issubstituted with one or more electron donating groups (where “bridge”means a molecular fragment that connects two or more chemical groups,“donor” means an atom or group of atoms with a low ionization potentialthat can be bonded to a conjugated it-electron bridge, and “acceptor”means an atom or group of atoms with a high electron affinity that canbe bonded to a conjugated π-electron bridge).

[0062] Representative examples of such photosensitizers include thefollowing:

[0063] The four classes of photosensitizers described above can beprepared by reacting aldehydes with ylides under standard Wittigconditions or by using the McMurray reaction, as detailed in WO98/21521.

[0064] Other suitable compounds are described in U.S. Pat. Nos.6,100,405, 5,859,251, and 5,770,737 as having large multi-photonabsorption cross-sections, although these cross-sections were determinedby a method other than that described above. Representative examples ofsuch compounds include the following:

(2) Electron Acceptor Compounds

[0065] Suitable electron acceptors for the multi-photon reactivecompositions are capable of being photosensitized by accepting anelectron from an electronic excited state of the multi-photonphotosensitizer, resulting in the formation of at least one free radicaland/or acid. Such electron acceptors include iodonium salts (forexample, diaryliodonium salts), chloromethylated triazines (for example,2-methyl-4,6-bis(trichloromethyl)-s-triazine,2,4,6-tris(trichloromethyl)-s-triazine, and2-aryl-4,6-bis(trichloromethyl)-s-triazine), diazonium salts (forexample, phenyldiazonium salts optionally substituted with groups suchas alkyl, alkoxy, halo, or nitro), sulfonium salts (for example,triarylsulfonium salts optionally substituted with alkyl or alkoxygroups, and optionally having 2,2′ oxy groups bridging adjacent arylmoieties), azinium salts (for example, an N-alkoxypyridinium salt), andtriarylimidazolyl dimers (preferably, 2,4,5-triphenylimidazolyl dimerssuch as 2,2′,4,4′,5,5′-tetraphenyl-1,1′-biimidazole, optionallysubstituted with groups such as alkyl, alkoxy, or halo), and the like,and mixtures thereof.

[0066] The electron acceptor is preferably soluble in the reactivespecies and is preferably shelf-stable (that is, does not spontaneouslypromote reaction of the reactive species when dissolved therein in thepresence of the photosensitizer and an electron donor compound).Accordingly, selection of a particular electron acceptor can depend tosome extent upon the particular reactive species, photosensitizer, andelectron donor compound chosen, as described above.

[0067] Suitable iodonium salts include those described in U.S. Pat. Nos.5,545,676, 3,729,313, 3,741,769, 3,808,006, 4,250,053 and 4,394,403. Theiodonium salt can be a simple salt (for example, containing an anionsuch as Cl—, Br—, I— or C₄H₅SO₃—) or a metal complex salt (for example,containing SbF₆—, PF₆—, BF₄—, tetrakis(perfluorophenyl)borate, SbF₅ OH—or AsF₆—). Mixtures of Iodonium salts can be used if desired.

[0068] Examples of useful aromatic iodonium complex salt electronacceptors include diphenyliodonium tetrafluoroborate;di(4-methylphenyl)iodonium tetrafluoroborate;phenyl-4-methylphenyliodonium tetrafluoroborate;di(4-heptylphenyl)iodonium tetrafluoroborate; di(3-nitrophenyl)iodoniumhexafluorophosphate; di(4-chlorophenyl)iodonium hexafluorophosphate;di(naphthyl)iodonium tetrafluoroborate;di(4-trifluoromethylphenyl)iodonium tetrafluoroborate; diphenyliodoniumhexafluorophosphate; di(4-methylphenyl)iodonium hexafluorophosphate;diphenyliodonium hexafluoroarsenate; di(4-phenoxyphenyl)iodoniumtetrafluoroborate; phenyl-2-thienyliodonium hexafluorophosphate;3,5-dimethylpyrazolyl-4-phenyliodonium hexafluorophosphate;diphenyliodonium hexafluoroantimonate; 2,2′-diphenyliodoniumtetrafluoroborate; di(2,4-dichlorophenyl)iodonium hexafluorophosphate;di(4-bromophenyl)iodonium hexafluorophosphate;di(4-methoxyphenyl)iodonium hexafluorophosphate;di(3-carboxyphenyl)iodonium hexafluorophosphate;di(3-methoxycarbonylphenyl)iodonium hexafluorophosphate;di(3-methoxysulfonylphenyl)iodonium hexafluorophosphate;di(4-acetamidophenyl)iodonium hexafluorophosphate;di(2-benzothienyl)iodonium hexafluorophosphate; and diphenyliodoniumhexafluoroantimonate; and the like; and mixtures thereof. Aromaticiodonium complex salts can be prepared by metathesis of correspondingaromatic iodonium simple salts (such as, for example, diphenyliodoniumbisulfate) in accordance with the teachings of Beringer et al., J. Am.Chem. Soc. 81, 342 (1959).

[0069] Preferred iodonium salts include diphenyliodonium salts (such asdiphenyliodonium chloride, diphenyliodonium hexafluorophosphate, anddiphenyliodonium tetrafluoroborate), diaryliodonium hexafluoroantimonate(for example, those available under the trade designation SARCAT SR 1012from Sartomer Company), and mixtures thereof.

[0070] Suitable anions, X—, for the sulfonium salts (and for any of theother types of electron acceptors) include a variety of anion types suchas, for example, imide, methide, boron-centered, phosphorous-centered,antimony-centered, arsenic-centered, and aluminum-centered anions.

[0071] Illustrative, but not limiting, examples of suitable imide andmethide anions include (C₂F₅SO₂)₂N⁻, (C₄F₉SO₂)₂N⁻, (C₈F₁₇SO₂)₃C⁻,(CF₃SO₂)₃C⁻, (CF₃SO₂)₂N⁻, (C₄F₉SO₂)₃C⁻, (CF₃SO₂)₂(C₄F₉SO₂)C⁻,(CF₃SO₂)(C₄F₉SO₂)N⁻, ((CF₃)₂NC₂F₄SO₂)₂N⁻, (CF₃)₂NC₂F₄SO₂C⁻(SO₂ CF₃)₂,(3,5-bis(CF₃)C₆H₃)SO₂N⁻SO₂CF₃, C₆H₅SO₂C⁻(SO₂CF₃)₂, C₆H₅SO₂N⁻SO₂CF₃, andthe like. Preferred anions of this type include those represented by theformula (R_(f)SO₂)₃C⁻, wherein R_(f) is a perfluoroalkyl radical havingfrom 1 to about 4 carbon atoms.

[0072] Illustrative, but not limiting, examples of suitableboron-centered anions include F₄B⁻, (3,5-bis(CF₃)C₆H₃)₄B⁻, (C₆F₅)₄B⁻,(p-CF₃C₆H₄)₄B⁻, (m-CF₃C₆H₄)₄B⁻, (p-FC₆H₄)₄B⁻,(C₆F₅)₃(CH₃)B⁻,(C₆F₅)₃(n-C₄H₉)B⁻, (p-CH₃C₆H₄)₃(C₆F₅)B⁻, (C₆F₅)₃FB⁻, (C₆H₅)₃₍C₆F₅)B⁻,(CH₃)₂(p-CF₃C₆H₄)₂B⁻, (C₆F₅)₃(n-C₁₈H₃₇O)B⁻, and the like. Preferredboron-centered anions generally contain 3 or more halogen-substitutedaromatic hydrocarbon radicals attached to boron, with fluorine being themost preferred halogen. Illustrative, but not limiting, examples of thepreferred anions include (3,5-bis(CF₃)C₆H₃)₄B⁻, (C₆F₅)₄B⁻,(C₆F₅)₃(n-C₄H₉)B⁻, (C₆F₅)₃FB⁻, and (C₆F₅)₃(CH₃)B⁻.

[0073] Suitable anions containing other metal or metalloid centersinclude, for example, (3,5-bis(CF₃)C₆H₃)₄Al⁻, (C₆F₅)₄Al⁻, (C₆F₅)₂F₄P⁻,(C₆F₅)F₅P⁻, F₆P⁻, (C₆F₅)F₅Sb⁻, F₆Sb⁻, (HO)F₅Sb⁻, and F₆As⁻. Preferably,the anion, X⁻, is selected from tetrafluoroborate, hexafluorophosphate,hexafluoroarsenate, hexafluoroantimonate, andhydroxypentafluoroantimonate (for example, for use withcationically-curable species such as epoxy resins).

[0074] Examples of suitable sulfonium salt electron acceptors include:

[0075] triphenylsulfonium tetrafluoroborate

[0076] methyldiphenylsulfonium tetrafluoroborate

[0077] dimethylphenylsulfonium hexafluorophosphate

[0078] triphenylsulfonium hexafluorophosphate

[0079] triphenylsulfonium hexafluoroantimonate

[0080] diphenylnaphthylsulfonium hexafluoroarsenate

[0081] tritolyesulfonium hexafluorophosphate

[0082] anisyldiphenylsulfonium hexafluoroantimonate

[0083] 4-butoxyphenyldiphenylsulfonium tetrafluoroborate

[0084] 4-chlorophenyldiphenylsulfonium hexafluorophosphate

[0085] tri(4-phenoxyphenyl)sulfonium hexafluorophosphate

[0086] di(4-ethoxyphenyl)methylsulfonium hexafluoroarsenate

[0087] 4-acetonylphenyldiphenylsulfonium tetrafluoroborate

[0088] 4-thiomethoxyphenyldiphenylsulfonium hexafluorophosphate

[0089] di(methoxysulfonylphenyl)methylsulfonium hexafluoroantimonate

[0090] di(nitrophenyl)phenylsulfonium hexafluoroantimonate

[0091] di(carbomethoxyphenyl)methylsulfonium hexafluorophosphate

[0092] 4-acetamidophenyldiphenylsulfonium tetrafluoroborate

[0093] dimethylnaphthylsulfonium hexafluorophosphate

[0094] trifluoromethyldiphenylsulfonium tetrafluoroborate

[0095] p-(phenylthiophenyl)diphenylsulfonium hexafluoroantimonate

[0096] 10-methylphenoxanthenium hexafluorophosphate

[0097] 5-methylthianthrenium hexafluorophosphate

[0098] 10-phenyl-9,9-dimethylthioxanthenium hexafluorophosphate

[0099] 10-phenyl-9-oxothioxanthenium tetrafluoroborate

[0100] 5-methyl-10-oxothianthrenium tetrafluoroborate

[0101] 5-methyl-10,10-dioxothianthrenium hexafluorophosphate

[0102] Preferred sulfonium salts include triaryl-substituted salts suchas triarylsulfonium hexafluoroantimonate (for example, those availableunder the trade designation SARCAT SR 1010 from Sartomer Company),triarylsulfonium hexafluorophosphate (for example, those available underthe trade designation SARCAT SR 1011 from Sartomer Company), andtriarylsulfonium hexafluorophosphate (for example, those available underthe trade designation SARCAT KI85 from Sartomer Company).

[0103] Useful azinium salts include those described in U.S. Pat. No.4,859,572 which include an azinium moiety, such as a pyridinium,diazinium, or triazinium moiety. The azinium moiety can include one ormore aromatic rings, typically carbocyclic aromatic rings (for example,quinolinium, isoquinolinium, benzodiazinium, and naphthodiazoniummoieties), fused with an azinium ring. A quaternizing substituent of anitrogen atom in the azinium ring can be released as a free radical uponelectron transfer from the electronic excited state of thephotosensitizer to the azinium electron acceptor. In one preferred form,the quaternizing substituent is an oxy substituent. The oxy substituent,—O-T, which quaternizes a ring nitrogen atom of the azinium moiety canbe selected from among a variety of synthetically convenient oxysubstituents. The moiety T can, for example, be an alkyl radical, suchas methyl, ethyl, butyl, and so forth. The alkyl radical can besubstituted. For example, aralkyl (for example, benzyl and phenethyl)and sulfoalkyl (for example, sulfomethyl) radicals can be useful. Inanother form, T can be an acyl radical, such as an —OC(O)-T¹ radical,where T¹ can be any of the various alkyl and aralkyl radicals describedabove. In addition, T¹ can be an aryl radical, such as phenyl ornaphthyl. The aryl radical can in turn be substituted. For example, T¹can be a tolyl or xylyl radical. T typically contains from 1 to about 18carbon atoms, with alkyl moieties in each instance above preferablybeing lower alkyl moieties and aryl moieties in each instance preferablycontaining about 6 to about 10 carbon atoms. Highest activity levelshave been realized when the oxy substituent, —O-T, contains 1 or 2carbon atoms. The azinium nuclei need include no substituent other thanthe quaternizing substituent. However, the presence of othersubstituents is not detrimental to the activity of these electronacceptors.

[0104] Useful triarylimidazolyl dimers include those described in U.S.Pat. No. 4,963,47 1. These dimers include, for example,2-(o-chlorophenyl)-4,5-bis(m-methoxyphenyl)-1,1′-biimidazole;2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenyl-1,1′-biimidazole; and2,5-bis(o-chlorophenyl)-4-[3,4-dimethoxyphenyl]-1,1′-biimidazole.

[0105] Preferred electron acceptors include photoacid generators, suchas iodonium salts (more preferably, aryliodonium salts),chloromethylated triazines, sulfonium salts, and diazonium salts. Morepreferred are aryliodonium salts and chloromethylated triazines.

(3) Electron Donor Compounds

[0106] Electron donor compounds useful in the multi-photonphotosensitizer system of the multi-photon reactive composition arecompounds (other than the photosensitizer itself) that are capable ofdonating an electron to an electronic excited state of thephotosensitizer. The electron donor compounds preferably have anoxidation potential that is greater than zero and less than or equal tothat of p-dimethoxybenzene. Preferably, the oxidation potential isbetween about 0.3 and 1 V vs. a standard saturated calomel electrode(“S.C.E.”).

[0107] The electron donor compound is also preferably soluble in thereactive species and is selected based in part upon shelf stabilityconsiderations (as described above). Suitable donors are generallycapable of increasing the speed of cure or the image density of aphotoreactive composition upon exposure to light of the desiredwavelength.

[0108] When working with cationically-reactive species, those skilled inthe art will recognize that the electron donor compound, if ofsignificant basicity, can adversely affect the cationic reaction. (See,for example, the discussion in U.S. Pat. No. 6,025,406.)

[0109] In general, electron donor compounds suitable for use withparticular photosensitizers and electron acceptors can be selected bycomparing the oxidation and reduction potentials of the three components(as described, for example, in U.S. Pat. No. 4,859,572). Such potentialscan be measured experimentally (for example, by the methods described byR. J. Cox, Photographic Sensitivity, Chapter 15, Academic Press (1973))or can be obtained from references such as N. L. Weinburg, Ed.,Technique of Electroorganic Synthesis Part II: Techniques of Chemistry,Vol. V (1975), and C. K. Mann and K. K. Barnes, ElectrochemicalReactions in Nonaqueous Systems (1970). The potentials reflect relativeenergy relationships and can be used in the manner described below toguide electron donor compound selection.

[0110] When the photosensitizer is in an electronic excited state, anelectron in the highest occupied molecular orbital (HOMO) of thephotosensitizer has been lifted to a higher energy level (namely, thelowest unoccupied molecular orbital (LUMO) of the photosensitizer), anda vacancy is left behind in the molecular orbital it initially occupied.The electron acceptor can accept the electron from the higher energyorbital, and the electron donor compound can donate an electron to fillthe vacancy in the originally occupied orbital, provided that certainrelative energy relationships are satisfied.

[0111] If the reduction potential of the electron acceptor is lessnegative (or more positive) than that of the photosensitizer, anelectron in the higher energy orbital of the photosensitizer is readilytransferred from the photosensitizer to the lowest unoccupied molecularorbital (LUMO) of the electron acceptor, since this represents anexothermic process. Even if the process is instead slightly endothermic(that is, even if the reduction potential of the photosensitizer is upto 0.1 volt more negative than that of the electron acceptor) ambientthermal activation can readily overcome such a small barrier.

[0112] In an analogous manner, if the oxidation potential of theelectron donor compound is less positive (or more negative) than that ofthe photosensitizer, an electron moving from the HOMO of the electrondonor compound to the orbital vacancy in the photosensitizer is movingfrom a higher to a lower potential, which again represents an exothermicprocess. Even if the process is slightly endothermic (that is, even ifthe oxidation potential of the photosensitizer is up to 0.1 V morepositive than that of the electron donor compound), ambient thermalactivation can readily overcome such a small barrier.

[0113] Slightly endothermic reactions in which the reduction potentialof the photosensitizer is up to 0.1 V more negative than that of theelectron acceptor, or the oxidation potential of the photosensitizer isup to 0.1 V more positive than that of the electron donor compound,occur in every instance, regardless of whether the electron acceptor orthe electron donor compound first reacts with the photosensitizer in itsexcited state. When the electron acceptor or the electron donor compoundis reacting with the photosensitizer in its excited state, it ispreferred that the reaction be exothermic or only slightly endothermic.When the electron acceptor or the electron donor compound is reactingwith the photosensitizer ion radical, exothermic reactions are stillpreferred, but still more endothermic reactions can be expected in manyinstances to occur. Thus, the reduction potential of the photosensitizercan be 0.2 V or more, more negative than that of a second-to-reactelectron acceptor, or the oxidation potential of the photosensitizer canbe 0.2 V or more, more positive than that of a second-to-react electrondonor compound.

[0114] Suitable electron donor compounds include, for example, thosedescribed by D. F. Eaton in Advances in Photochemistry, edited by B.Voman et al., Volume 13, pp. 427-488, John Wiley and Sons, New York(1986); U.S. Pat. Nos. 6,025,406, and 5,545,676. Such electron donorcompounds include amines (including triethanolamine, hydrazine,1,4-diazabicyclo[2.2.2]octane, triphenylamine (and itstriphenylphosphine and triphenylarsine analogs), aminoaldehydes, andaminosilanes), amides (including phosphoramides), ethers (includingthioethers), ureas (including thioureas), sulfinic acids and theirsalts, salts of ferrocyanide, ascorbic acid and its salts,dithiocarbamic acid and its salts, salts of xanthates, salts of ethylenediamine tetraacetic acid, salts of (alkyl)_(n)(aryl)_(m)borates (n+m=4)(tetraalkylammonium salts preferred), various organometallic compoundssuch as SnR₄ compounds (where each R is independently chosen from amongalkyl, aralkyl (particularly, benzyl), aryl, and alkaryl groups) (forexample, such compounds as n-C₃H₇Sn(CH₃)₃, (allyl)Sn(CH₃)₃, and(benzyl)Sn(n-C₃H₇)₃), ferrocene, and the like, and mixtures thereof. Theelectron donor compound can be unsubstituted or can be substituted withone or more non-interfering substituents. Particularly preferredelectron donor compounds contain an electron donor atom (such as anitrogen, oxygen, phosphorus, or sulfur atom) and an abstractablehydrogen atom bonded to a carbon or silicon atom alpha to the electrondonor atom.

[0115] Preferred amine electron donor compounds include alkyl-, aryl-,alkaryl- and aralkyl-amines (for example, methylamine, ethylamine,propylamine, butylamine, triethanolamine, amylamine, hexylamine,2,4-dimethylaniline, 2,3-dimethylaniline, o-, m- and p-toluidine,benzylamine, aminopyridine, N,N′-dimethylethylenediamine,N,N′-diethylethylenediamine, N,N′-dibenzylethylenediamine,N,N′-diethyl-1,3-propanediamine, N,N′-diethyl-2-butene-1,4-diamine,N,N′-dimethyl-1,6-hexanediamine, piperazine,4,4′-trimethylenedipiperidine, 4,4′-ethylenedipiperidine,p-N,N-dimethyl-aminophenethanol and p-N-dimethylaminobenzonitrile);aminoaldehydes (for example, p-N,N-dimethylaminobenzaldehyde,p-N,N-diethylaminobenzaldehyde, 9-julolidine carboxaldehyde, and4-morpholinobenzaldehyde); and aminosilanes (for example,trimethylsilylmorpholine, trimethylsilylpiperidine,bis(dimethylamino)diphenylsilane, tris(dimethylamino)methylsilane,N,N-diethylaminotrimethylsilane, tris(dimethylamino)phenylsilane,tris(methylsilyl)amine, tris(dimethylsilyl)amine,bis(dimethylsilyl)amine, N,N-bis(dimethylsilyl)aniline,N-phenyl-N-dimethylsilylaniline, and N,N-dimethyl-N-dimethylsilylamine);and mixtures thereof. Tertiary aromatic alkylamines, particularly thosehaving at least one electron-withdrawing group on the aromatic ring,have been found to provide especially good shelf stability. Good shelfstability has also been obtained using amines that are solids at roomtemperature. Good photographic speed has been obtained using amines thatcontain one or more julolidinyl moieties.

[0116] Preferred amide electron donor compounds includeN,N-dimethylacetamide, N,N-diethylacetamide, N-methyl-N-phenylacetamide,hexamethylphosphoramide, hexaethylphosphoramide,hexapropylphosphoramide, trimorpholinophosphine oxide,tripiperidinophosphine oxide, and mixtures thereof.

[0117] Preferred alkylarylborate salts include

[0118] Ar₃B⁻(n-C₄H₉)N⁺(C₂H₅)₄

[0119] Ar₃B⁻(n-C₄H₉)N⁺(CH₃)₄

[0120] Ar₃B⁻(n-C₄H₉)N⁺(n-C₄H₉)₄

[0121] Ar₃B⁻(n-C₄H₉)Li⁺

[0122] Ar₃B⁻(n-C₄H₉)N⁺(C₆H₁₃)₄

[0123] Ar₃B⁻—(C₄H₉)N⁺(CH₃)₃(CH₂)₂CO₂(CH₂)₂CH₃

[0124] Ar₃B⁻—(C₄H₉)N⁺(CH₃)₃(CH₂)₂OCO(CH₂)₂CH₃

[0125] Ar₃B⁻-(sec-C₄H₉)N⁺(CH₃)₃(CH₂)₂CO₂(CH₂)₂CH₃

[0126] Ar₃B⁻-(sec-C₄H₉)N⁺(C₆H₁₃)₄

[0127] Ar₃B⁻—(C₄H₉)N⁺(C₈H₁₇)₄

[0128] Ar₃B⁻—(C₄H₉)N⁺(CH₃)₄

[0129] (p-CH₃)—C₆H₄)₃B⁻(n-C₄H₉)N⁺(n-C₄H₉)₄

[0130] Ar₃B⁻—(C₄H₉)N⁺(CH₃)₃(CH₂)₂OH

[0131] ArB⁻(n-C₄H₉)₃N⁺(CH₃)₄

[0132] ArB⁻(C₂H₅)₃N⁺(CH₃)₄

[0133] Ar₂B⁻(n-C₄H₉)₂N⁺(CH₃)₄

[0134] Ar₃B⁻(C₄H₉)N⁺(C₄H₉)₄

[0135] Ar₄B⁻N⁺(C₄H₉)₄

[0136] ArB⁻(CH₃)₃N⁺(CH₃)₄

[0137] (n-C₄H₉)₄B⁻N⁺(CH₃)₄

[0138] Ar₃B⁻(C₄H₉)P⁺(C₄H₉)₄

[0139] where Ar is phenyl, naphthyl, substituted (preferably,fluoro-substituted) phenyl, substituted naphthyl, and like groups havinggreater numbers of fused aromatic rings, as well as tetramethylammoniumn-butyltriphenylborate and tetrabutylammoniumn-hexyl-tris(3-fluorophenyl)borate (available under the tradedesignations CGI 437 and CGI 7460 from Ciba Specialty ChemicalsCorporation), and mixtures thereof.

[0140] Suitable ether electron donor compounds include4,4′-dimethoxybiphenyl, 1,2,4-trimethoxybenzene,1,2,4,5-tetramethoxybenzene, and the like, and mixtures thereof.Suitable urea electron donor compounds include N,N′-dimethylurea,N,N-dimethylurea, N,N′-diphenylurea, tetramethylthiourea,tetraethylthiourea, tetra-n-butylthiourea, N,N-di-n-butylthiourea,N,N′-di-n-butylthiourea, N,N-diphenylthiourea,N,N′-diphenyl-N,N′-diethylthiourea, and the like, and mixtures thereof.

[0141] Preferred electron donor compounds for free radical-inducedreactions include amines that contain one or more julolidinyl moieties,alkylarylborate salts, and salts of aromatic sulfinic acids. However,for such reactions, the electron donor compound can also be omitted, ifdesired (for example, to improve the shelf stability of thephotoreactive composition or to modify resolution, contrast, andreciprocity). Preferred electron donor compounds for acid-inducedreactions include 4-dimethylaminobenzoic acid, ethyl4-dimethylaminobenzoate, 3-dimethylaminobenzoic acid,4-dimethylaminobenzoin, 4-dimethylaminobenzaldehyde,4-dimethylaminobenzonitrile, 4-dimethylaminophenethyl alcohol, and1,2,4-trimethoxybenzene.

[0142] It is within the scope of this invention that either the electrondonor, the electron acceptor, or both can be covalently tethered to themulti-photon sensitizer.

Inorganic Particles

[0143] Particles suitable for use in the compositions of the inventionare described, for example, in U.S. Pat. No. 5,648,407, the descriptionof which is incorporated herein by reference. Suitable particles aremicron or sumicron in size, substantially inorganic in chemicalcomposition, and if used at concentrations greater than about 10% byweight in the composition, largely transparent at the wavelength oflight used for reaction of the multiphoton reactive composition. Suchparticles include but are not limited to metal oxides (such as Al₂O₃,ZrO₂, TiO₂, ZnO, SiO₂, and silicate glasses), metals, and metals alloys,as well as other sufficiently transparent non-oxide ceramic materials.An additional consideration in choosing the inorganic particle(s) can bethe temperature at which the material can be sintered into a denseinorganic structure.

[0144] Colloidal silica is the preferred particle for use in theinvention, but other colloidal metal oxides (for example, titania,alumina, zirconia, vanadia, antimony oxide, tin oxide, and mixturesthereof) can also be utilized. The colloidal particles can includeessentially a single oxide with sufficient transparency, such as silica,or can include a core of an oxide of one type (or a core of a materialother than a metal oxide) on which is deposited an oxide of anothertype, preferably silica. Alternatively colloidal particles can becomposed of clusters of smaller particles. Generally, the particles orclusters are smaller than the wavelength of light used forphotopatterning the composition and can range in size (average particlediameter) from about 10 nanometers to about 10 micron, preferably fromabout 10 nanometers to about 500 nanometers, more preferably from about10 nanometers to about 150 nanometers. Incorporation of colloidalparticles having the specified size range into the photoreactivecomposition yields a substantially clear, homogeneous composition. Suchcompositions minimize scattering of light during the photopatterningprocess.

[0145] Small amounts of other types of particles can be added to thecompositions in order to impart additional properties and/or function tothe fabricated structure. Such particles include, but are not limitedto, absorbing particles; particles with magnetic, dielectric,insulating, piezoelectric, ferroelectric, photochromic, refractory,chemically active, biocompatible, or luminescent properties; andparticles for enhancing mechanical strength and toughness. Examples ofsuch functional ceramic particles include MnFe₂O₄, SmCoO₅, NdFeB,PbZr_(0.5)Ti_(0.5)O₃, BaFe₁₂O₁₉, BaTiO₃, SrTiO₃, MoO₃, WO₃, SiC, Si₃N₄,MoS₂, Fe₂O₃, Fe₃O₄, and Ca₅(PO₄)₃OH. Ceramic particles can be obtainedcommercially (for example, from TPL (Technologies to Products),Albuquerque, N. Mex.; Materials Modification, Inc., Fairfax, Va.; andNanophase Technologies Corporation, Burr Bridge, Ill.) or fabricatedusing techniques known to those skilled in the art and/or described inthe pertinent texts and literature (see, for example, R. A. Andrievsky,“State-of-the-art and perspectives in the field of particulatenanostructured materials,” J. Mater Sci. Technol. 14 97 (1988)). Otheruseful non-ceramic particles include magnetic metals and metal alloysincluding Co, CoPt intermetallics (CoPt₃, CoPt, Co₃Pt), FePtintermetallics (Fe₃Pt, FePt, and FePt₃), CoNi, NiFe, CoFe and ternaryalloys of Co/Fe/Ni. The magnetic metal or metal alloy particles can havea shell of a second material such as silver to protect them fromoxidation. Such magnetic particles can be prepared for example usingtechniques described in European Patent Application No. EP 0,977,212 A.

[0146] It will be apparent to one skilled in the art that certain typesof inorganic particles can interact with components of the multiphotonphotoinitiator system (for example acting as an electron acceptor) andinterfere with the multiphoton-photoinitiated photoreaction. Thereforethe combination of the particular inorganic particles and themultiphoton photoinitiators can preferably be chosen to avoid suchinterference.

[0147] It is also preferable that the colloidal particles be relativelyuniform in size and remain substantially non-aggregated, as particleaggregation can result in precipitation, gellation, or a dramaticincrease in sol viscosity. Photoreactive compositions includingparticles having a substantially monodisperse or a substantially bimodalsize distribution are preferred. Thus, a particularly desirable class ofparticles for use in preparing the compositions of the invention includesols of inorganic particles (for example, colloidal dispersions ofinorganic particles in liquid media), especially sols of amorphoussilica. Such sols can be prepared by a variety of techniques and in avariety of forms, which include hydrosols (where water serves as theliquid medium), organosols (where organic liquids are used), and mixedsols (where the liquid medium includes both water and an organicliquid). See, for example, the descriptions of the techniques and formsgiven in U.S. Pat. Nos. 2,801,185 (Iler) and 4,522,958 (Das et al.),which descriptions are incorporated herein by reference, as well asthose given by R. K. Iler in The Chemistry of Silica, John Wiley & Sons,New York (1979).

[0148] Due to their surface chemistry and commercial availability,silica hydrosols are preferred for use in preparing the compositions ofthe invention. Such hydrosols are available in a variety of particlesizes and concentrations from, for example, Nyacol Products, Inc. inAshland, Md.; Nalco Chemical Company in Oakbrook, Ill.; and E. I. dupontde Nemours and Company in Wilmington, Del. Concentrations from about 10to about 50 percent by weight of silica in water are generally useful,with concentrations of from about 30 to about 50 weight percent beingpreferred (as there is less water to be removed). If desired, silicahydrosols can be prepared, for example, by partially neutralizing anaqueous solution of an alkali metal silicate with acid to a pH of about8 or 9 (such that the resulting sodium content of the solution is lessthan about 1 percent by weight based on sodium oxide). Other methods ofpreparing silica hydrosols, for example, electrodialysis, ion exchangeof sodium silicate, hydrolysis of silicon compounds, and dissolution ofelemental silicon are described by Iler, supra.

[0149] Preparation of the reactive resin sol generally requires that atleast a portion of the surface of the inorganic particles be modified soas to aid in the dispersibility of the particles in the resin. Thissurface modification can be effected by various different methods whichare known in the art. (See, for example, the surface modificationtechniques described in U.S. Pat. Nos. 2,801,185 (Iler) and 4,522,958(Das et al.), which descriptions are incorporated herein by reference).

[0150] For example, silica particles can be treated with monohydricalcohols, polyols, or mixtures thereof (preferably, a saturated primaryalcohol) under conditions such that silanol groups on the surface of theparticles chemically bond with hydroxyl groups to produce surface-bondedester groups. The surface of silica (or other metal oxide) particles canalso be treated with organosilanes, for example, alkyl chlorosilanes,trialkoxy arylsilanes, or trialkoxy alkylsilanes, or with other chemicalcompounds, for example, organotitanates, which are capable of attachingto the surface of the particles by a chemical bond (covalent or ionic)or by a strong physical bond, and which are chemically compatible withthe chosen resin(s). Treatment with organosilanes is generallypreferred. When aromatic ring-containing epoxy resins are utilized,surface treatment agents which also contain at least one aromatic ringare generally compatible with the resin and are thus preferred.Similarly other metal oxides can be treated with organic acids, (forexample, oleic acid), or the organic acid can be incorporated into thecomposition as a dispersant.

[0151] In preparing the reactive resin sols, a hydrosol (for example, asilica hydrosol) can generally be combined with a water-miscible organicliquid (for example, an alcohol, ether, amide, ketone, or nitrile) and,optionally (if alcohol is used as the organic liquid), a surfacetreatment agent such as an organosilane or organotitanate. Alcoholand/or the surface treatment agent can generally be used in an amountsuch that at least a portion of the surface of the particles is modifiedsufficiently to enable the formation of a stable reactive resin sol(upon combination with reactive resin). Preferably, the amount ofalcohol and/or treatment agent is selected so as to provide particleswhich are at least about 50 weight percent metal oxide (for example,silica), more preferably, at least about 75 weight percent metal oxide.(Alcohol can be added in an amount sufficient for the alcohol to serveas both diluent and treatment agent.) The resulting mixture can then beheated to remove water by distillation or by azeotropic distillation andcan then be maintained at a temperature of, for example, about 100° C.for a period of, for example, about 24 hours to enable the reaction (orother interaction) of the alcohol and/or other surface treatment agentwith chemical groups on the surface of the particles. This provides anorganosol comprising particles which have surface-attached orsurface-bonded organic groups (also referred to herein as “substantiallyinorganic” particles).

[0152] The resulting organosol can then be combined with a reactiveresin and the organic liquid removed by, for example, using a rotaryevaporator. Preferably, the organic liquid is removed by heating undervacuum to a temperature sufficient to remove even tightly-bound volatilecomponents. Stripping times and temperatures can generally be selectedso as to maximize removal of volatiles while minimizing advancement ofthe resin. Alternatively, methods known in the art such as ball milling,3-roll milling, Brabender mixing, extruding or any other high shearmixing process can be used to mix the inorganic particles with thereactive species.

Preparation of Multi-Photon Reactive Composition

[0153] The reactive and optionally non-reactive species, inorganicparticles, multi-photon photosensitizers, electron donor compounds, andelectron acceptors can be prepared by the methods described above or byother methods known in the art, and many are commercially available.These components can be combined under “safe light” conditions using anyorder and manner of combination (optionally, with stirring oragitation), although it is sometimes preferable (from a shelf life andthermal stability standpoint) to add the electron acceptor last (andafter any heating step that is optionally used to facilitate dissolutionof other components). Solvent can be used, if desired, provided that thesolvent is chosen so as to not react appreciably with the components ofthe composition. Suitable solvents include, for example, acetone,dichloroethane, and acetonitrile. The reactive species itself can alsosometimes serve as a solvent for the other components.

[0154] The components of the multi-photon photoinitiator system arepresent in photochemically effective amounts (as defined above).Generally, the multi-photon reactive composition contains from about 5%to about 99.79% by weight of one or more reactive species from about0.01% to about 10% by weight of one or more photosensitizers(preferably, from about 0.1% to about 5%; more preferably, from about0.2% to about 2%); up to about 10% by weight of one or more electrondonor compounds (preferably, from about 0.1% to about 10%; morepreferably, from about 0.1% to about 5%); and from about 0.1% to about10% by weight of one or more electron acceptors (preferably, from about0.1% to about 5%) based upon the total weight of solids in thecomposition (that is, the total weight of components other thansolvent).

[0155] The photoreactive composition is loaded with between 0.01% and 75% by volume of inorganic particles.

[0156] A wide variety of additives can be included in the multi-photonreactive compositions, depending upon the desired end use. Suitableadditives include solvents, diluents, resins, binders, plasticizers,pigments, dyes, thixotropic agents, indicators, inhibitors, stabilizers,ultraviolet absorbers, medicaments (for example, leachable fluorides),and the like. The amounts and types of such additives and their mannerof addition to the compositions will be familiar to those skilled in theart.

[0157] It is within the scope of this invention to include nonreactivepolymeric binders in the compositions in order, for example, to controlviscosity and to provide film-forming properties. Such polymeric binderscan generally be chosen to be compatible with the reactive species. Forexample, polymeric binders that are soluble in the same solvent that isused for the reactive species, and that are free of functional groupsthat can adversely affect the course of reaction of the reactivespecies, can be utilized. Binders can be of a molecular weight suitableto achieve desired film-forming properties and solution rheology (forexample, molecular weights between about 5,000 and 1,000,000 daltons;preferably between about 10,000 and 500,000 daltons; more preferably,between about 15,000 and 250,000 daltons). Suitable polymeric bindersinclude, for example, polystyrene, poly(methyl methacrylate),poly(styrene)-co-(acrylonitrile), cellulose acetate butyrate, and thelike. Suitable nonreactive polymeric binders, if present, can beincluded in the compositions up to 90%; preferably up to 75%; morepreferably up to 60% by weight of the total composition.

[0158] Prior to exposure, the multiphoton reactive compositions can beapplied on a substrate, if desired, by any of a variety of applicationmethods. The compositions can be applied by coating methods such asspin, knife, bar, reverse roll, and knurled roll coating, or byapplication methods such as dipping, immersion, spraying, brushing,curtain coating and the like. Alternatively, the composition can beapplied drop-wise. The substrate can be made of any suitable material(e.g., glass, fused silica, or silicon) and can be chosen from a widevariety of films, sheets, and other surfaces, depending upon theparticular application and the method of exposure to be utilized.

EXAMPLES

[0159] Unless otherwise noted, chemicals used in the examples werecommercially available from Aldrich Chemical Co., Milwaukee, Wis. Boratesalt was commercially available from Ciba Specialty Chemicals,Tarrytown, N.Y. under the trade designation CGI 7460. Diaryliodoniumhexafluoroantimonate salt was commercially available from SartomerCompany,West Chester, Pa. under the trade designation CD1012. Allpreparations were performed under safe lights to prevent prematurecuring of the compositions.

Preparatory Example 1

[0160] The two-photon sensitizing dye,bis-[4-(diphenylamino)stryl]-1-(2-ethylhexyloxy),4-(methoxy)benzene wasprepared as follows:

1-methoxy-4-(2-ethylhexyloxy)benzene (1)

[0161] A mixture of 4-methoxyphenol (100.0 g, 0.8 mol), dry potassiumcarbonate (166.7 g, 1.2 mol), acetonitrile (800 mL), and 2-ethylhexylbromide (173.8 g, 0.9 mol) was stirred mechanically and heated at refluxfor 4 days. After cooling, the mixture was diluted with water (1.5 L),and then the organic phase was separated. The aqueous layer wasextracted with hexane, and the combined organic layers were washed twotimes with 1.0 M NaOH and water. After drying over MgSO₄, the solventwas removed under reduced pressure to give an orange oil. The crudeproduct was distilled under reduced pressure to give 152 g (80%) of aclear oil. (bp 135-138° C. at 0.4 mmHg).

2,5-bis(bromomethyl)-1-methoxy-4-(2-ethylhexyloxy)benzene (2)

[0162] A mixture of 1-methoxy-4-(2-ethylhexyloxy)benzene (50.0 g, 0.21mol), paraformaldehyde (30.0 g, 1 mol), acetic acid (100 mL), and HBr(30% in acetic acid, 100 mL) was heated to 70° C. The reactionexothermed to 80° C. and the paraformaldehyde dissolved completely togive an orange solution. After 4 h at 70° C., the reaction was cooled toroom temperature. The mixture was diluted with methylene chloride (500mL), and the organic layer was washed three times with water and oncewith saturated NaHCO₃. After drying over MgSO₄, the solvent was removedunder vacuum. A pale yellow solid was obtained which was recrystallizedfrom hexane to give a yellow/white powder (71.6 g, 81 %).

[0163] Alternatively:2,5-bis(choloromethyl)-1-methoxy-4-(2-ethylhexyloxy)benzene can besynthesized according to procedures in U.S. Pat. No. 5,189,136.

Phosphine Derivative (3)

[0164] A mixture of2,5-bis(chloromethyl)-1-methoxy-4-(2-ethylhexyloxy)benzene (28.26 g, 85mmol) and triethyl phosphite (37.4 g, 0.23 mol) was heated to reflux for6 h. After cooling, the product was heated under high vacuum to removeresidual triethylphosphite. A thick oil was obtained which slowlycrystallized after several days and was used without furtherpurification in the following step.

Bis-[4-(diphenylamino)stryl]-1-(2-ethylhexyloxy),4-(methoxy)benzene (4)

[0165] To a mixture of phosphine derivative (3) (11.60 g, 21.7 mmol),4-diphenylaminobenzaldehyde (12.34 g, 45.1 mmol), and drytetrahydrofuran (400 mL) was added dropwise potassium t-butoxide (1.0 Min tetrahydrofuran, 44 mL, 44 mmol). The mixture was stirred for 3 hoursat room temperature, then the solvent was removed under vacuum. Water(100 mL) was added to the residue, and the mixture was extracted severaltimes with methylene chloride. The combined organic layers were washedwith brine, dried over MgSO₄ and the solvent was removed under vacuum.The crude product was purified by column chromatography on silica gelusing 30/70 methylene chloride/hexane to give a bright green solid(14.44 g, 86%).

Preparatory Example 2

[0166] Preparation of the silica-epoxy sol is described. 100 g of NALCO2327 (approximately 41% aqueous dispersion) from Ondeo Nalco(Naperville, Ill.) was placed in a round bottom flask. A premixedsolution of 225 grams of 1-methoxy-2-propanol and 5.04 grams oftrimethoxyphenylsilane (0.62 mmols of silane per gram of silica) wasadded under medium agitation over a period of 5-10 minutes. Theresulting non-agglomerated solution was heated at 90-95° C. forapproximately 22 hours and then dried to yield a white, powder. Thetreated silica was added to de-ionized water (100 g silica to 300 g ofwater), vigorously stirred for 3-4 hours, and then allowed to sit atroom temperature overnight. The silica was filtered off, washed wellwith additional rinses of de-ionized water, and dried.

[0167] The treated silica was dispersed in acetone (20-25% solids) usinga high shear Silverson L4R mixer set at ¾ speed for 5 minutes. Theresulting dispersion was covered and allowed to sit for a minimum of twohours. The dispersion was filtered through one micron Gelman acrodisc,25 mm glass fiber syringe filters, and the percent silica solidsdetermined.

[0168] A sample of the above silica/acetone mixture containing 10 g ofsilica was added to 4.87 g of cycloaliphatic epoxy resin available fromDow Chemical (Midland, Mich.) under the trade designation ERL-422 1,mixed well and vacuum stripped while slowly heating using a rotaryevaporator and oil bath and maintained at a final stripping temperatureof 130° C. for 30 minutes. 0.26 grams of 1,4 butanediol and 1.54 g ofHELOXY 107 (Shell Chemical) were then added to this high viscositymixture and mixed for 5 minutes at 3000 rpm using a FlackTek Inc. 150FVZ speed mixer to give a silica-epoxy sol containing 60% silica byweight.

Example 3

[0169] 7.5 g of the silica-epoxy sol prepared in Example 2 was combinedwith a solution of 0.075 g of CD1012 and 0.036 g ofBis-[4-(diphenylamino)stryl]-1-(2-ethylhexyloxy),4-(methoxy)benzene(from example 1) dissolved in 0.25 g tetrahydrofuran (Burdick & Jackson,Muskegon, Mich.) and 1.0 g of 1,2-dichloroethane. The solution was speedmixed at 3000 rpm for 90 seconds using a FlackTek Inc. 150 FVZ speedmixer and then spin coated on to silicon wafer that had been pre-treatedwith 2-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane (Gelest, Tullytown,Pa.). The coated wafers were then soft baked in an 80° C. oven for 30minutes to remove the residual solvent. The uncured film thickness wasapproximately 60 microns.

[0170] Two-photon polymerization was performed using a diode pumpedTi:sapphire laser (Spectra-Physics) operating at a wavelength of 800 nm,pulse width 100 fs, pulse repetition rate of 80 MHz, and beam diameterof approximately 5 mm. The optical train consisted of low dispersionturning mirrors, a beam expander, an optical attenuator to vary theoptical power, and a 60× microscope objective (NA 0.85) to focus thelight into the sample. The average power delivered to the sample was 16mW. The position of the microscope objective was adjusted to set thefocal point at the resin/wafer interface. The substrate was movedunderneath the focused beam at nominally 170 mm/min using a computercontrolled, 3-axis stage to expose an array of 20 micron wide bars with20 micron spacing. A second layer of perpendicular bars was exposed 15microns above the first layer. Each individual bar was exposed by rasterscanning the stage and moving over by one micron after each pass.

[0171] A second coated wafer was exposed at nominally 240 mm/min in apattern to form a 3 layer pyramid-like structure. The dimensions of thebottom layer that was attached to the substrate was 0.25 mm by 0.25 mm.For each successive layer z-axis position was moved up by 15 microns andthe length and width were adjusted to be 80% of the previous layer. Eachlayer was created by raster scanning the stage, moving over by onemicron after each pass.

[0172] Following exposure, both wafers were baked on a 110° C. hot platefor 5 minutes and then the unreacted resin was removed by development inpropylene glycol methyl ether acetate and isopropanol rinse. The sampleswere lightly coated with AuPd and examined using a scanning electronmicroscope. The developed nanocomposite lattice structures had goodstructural integrity. The undercuts were clearly visible and the widthof the lines was within 10% of the specified target dimensions. Thepyramid-like structures also showed good dimensional fidelity. A slightlip was observed on two-sides of each layer that was attributed toacceleration and deceleration of the stages during raster scanning.

Example 4

[0173] In this example, sintering of two-photon polymerized resins toform a completely inorganic three-dimensional structure is demonstrated.The lattice structures created in example 3 were heated in air at 1°C./min to 700° C., in a Vulcan furnace (Model #3-350 Degussa-Ney,Bloomfield, Conn.) maintained at 700° C. for 2 hours, and then slowlycooled to room temperature. They were then re-examined using a scanningelectron microscope.

[0174] The three-dimensional lattice structure including the undercutswas observed to be intact.

Example 5

[0175] This example describes the fabrication of a polymer magneticmicroactuator.

Resin Preparation

[0176] SR9008 is a trifunctional acrylate ester available from SartomerCompany (West Chester, Pa.). SR368 is tris(2-hydroxyethyl) isocyanuratetriacrylate that is commercially available from Sartomer Company (WestChester, Pa.). NANOCAT™ magnetic iron oxide is a free flowing powder of40-60 nm diameter nanoparticles that is commercially available from MachI (King of Prussia, Pa.).

Stock Solution A

[0177] 16.25% PMMA (120,000 g/mol, Aldrich), 19.0% of SR9008, 19.0 %SR368, 0.25%Bis-[4-(diphenylamino)stryl]-1-(2-ethylhexyloxy),4-(methoxy)benzene (4),0.5% CD1012, and 45% 1,2-dichloroethane by weight are combined andstirred until a homogeneous solution is obtained. This mixture isreferred to as stock solution A.

Stock Solution B

[0178] 42% of SR9008, 42% SR368, 15% NANOCAT™, and 1% oleic acid(Aldrich) by weight are combined and then blended on a 3 roll mill untilno large particulates are present and the resin appears transparent. Theresulting mixture is referred to as stock solution B.

Stock Solution C

[0179] 20 % PMMA (120,000 g/mol, and 79.34% Aldrich), 0.66% Irgacure 819(Ciba, Tarrytown, N.Y.) 1,2-dichloroethane by weight are combined andallowed to stir until the catalyst is thoroughly dispersed. 15 g of thissolution is combined with 7 g of stock solution B and blended on a 3roll mill until a homogenous mixture is obtained. The resulting solutionis collected as stock solution C.

Spin Coating and Magnetization

[0180] Thin silicon wafers are cleaned by soaking them for 10 minutes ina 3:1 mixture of sulfuric acid (98% solution) and hydrogen peroxide (30%solution in H₂O), followed by thorough rinsing with deionized water,rinsing again with isopropanol, and then blown dry. To promote adhesionof the curable composition to the silicon surface, the cleaned siliconwafers are dip coated in a 2% by weight solution of3-(trimethoxysilyl)propyl methacrylate in slightly acidic (pH 4-5)aqueous ethanol (190 proof). The slides are rinsed briefly in anhydrousethanol, cured for 10 minutes in a 130° C. oven, and then allowed tocool.

[0181] A portion of stock solution A is dispensed onto a primed siliconwafer and spin coated to form a uniform film, approximately 40 micronsthick. The coated wafer is soft baked in an oven to remove the residualsolvents (approximately 2 hours at 80° C.), and then cooled to roomtemperature. A portion of stock solution B is dispensed onto the dried,coated, wafer and spin coated to form a second layer approximately 10microns thick on top of the first layer. The wafer is then soft bakedagain in an oven to remove the residual solvents and remove stresses inthe film.

[0182] The coated wafer is then placed between the poles of a permanentmagnet such that the magnetic field lines are parallel to the substrate.The assembly is placed in a 50° C. oven for 24 hours to allow themagnetic nanoparticles to align with the field and then cooled to roomtemperature. The coated wafer is then removed for the assembly. Thepermanent magnet has a magnetic field strength of at least 0.5 Tesla andan operating temperature of at least 80° C.

Exposure

[0183] Two-photon polymerization is performed using a tunable diodepumped Ti:sapphire laser (Spectra-Physics) operating at a wavelength of800 nm, pulse width 100 fs, pulse repetition rate of 80 MHz, beamdiameter of approximately 5 mm. The optical train consists of lowdispersion turning mirrors, a beam expander, an optical attenuator tovary the optical power, and a 100× oil immersion microscope objective(NA 1.25) to focus the light into the sample. The average powerdelivered to the sample is 1.5 mW. The position of the microscopeobjective is adjusted to set the focal point at the resin/waferinterface. Referring to FIGS. 3A-3B, the coated wafer is movedunderneath the focused beam at 50 mm/min using a computer controlled,3-axis stage to form the body 505, flexible prongs 518 and 520, andextension region 512. The height of the body is 40 microns. The laseroutput is then tuned to 755 nm and the average power adjusted toapproximately 50 mW. The substrate is moved under the focused beam at 10mm/min to form the cured structure 517. The height of the cured region517 is 10 microns. The exposed wafer is then developed in propyleneglycol methyl ether acetate and allowed to dry slowly at roomtemperature.

[0184] The wafer and microstructure are placed on top of anelectromagnet and aligned so that the microstructure 500 isapproximately aligned in the center. The microactuator is observed undera microscope as the current supplied to the electomagnet is slowlyincreased. The flexible prongs 518 and 520, and extension region 512,are observed to deflect out of plane as the current is increased. Theelectromagnet is removed and a permanent bar magnet is slowly broughtclose to the undersurface of the wafer. The microactuator is observedunder a microscope as one pole of the bar magnet approaches the bottomof the wafer. The flexible prongs 518 and 520, and extension region 512,are observed to deflect in and out of plane as the magnet is moved toand away from the structure.

[0185] A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications can bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A multi-photon reactive composition comprising:(a) at least one reactive species; (b) a multi-photon photoinitiatorsystem; and (c) a plurality of substantially inorganic particles,wherein the particles have an average particle size of less than about10 microns in diameter.
 2. The multi-photon reactive composition ofclaim 1, wherein the particles are substantially monodisperse in size.3. The multi-photon reactive composition of claim 1, wherein theparticles are substantially bimodal in size distribution.
 4. Themulti-photon reactive composition of claim 1, wherein the particles havebeen surface treated.
 5. The multi-photon reactive composition of claim4, wherein the surface treatment is selected from the group consistingof silanization, plasma treatment, Corona treatment, organic acid,hydrolysis, coating, and titanation.
 6. The multi-photon reactivecomposition of claim 1, wherein the photoinitiator system comprises amulti-photon photosensitizer and an electron acceptor.
 7. Themulti-photon reactive composition of claim 6, wherein the system furthercomprises an electron donor.
 8. The multi-photon reactive composition ofclaim 6, wherein the multi-photon photosensitizer has a two-photonabsorption cross-section greater than that of fluorescein.
 9. Themulti-photon reactive composition of claim 6, wherein the multi-photonphotosensitizer has a two-photon absorption cross-section at least 1.5times greater than that of fluorescein.
 10. The multi-photon reactivecomposition of claim 6, wherein the photosensitizer is capable ofsensitizing 2-methyl-4,6-bis(trichloromethyl)-s-triazine undercontinuous irradiation in a wavelength range that overlaps the singlephoton absorption spectrum of the photosensitizer using the testprocedure described in U.S. Pat. No. 3,729,313.
 11. The multi-photonreactive composition of claim 6, wherein the photosensitizer is selectedfrom Rhodamine B and (a) molecules in which two donors are connected toa conjugated π (pi)-electron bridge; (b) molecules in which two donorsare connected to a conjugated π (pi)-electron bridge which issubstituted with one or more electron accepting groups; (c) molecules inwhich two acceptors are connected to a conjugated π (pi)-electronbridge; and (d) molecules in which two acceptors are connected to aconjugated π (pi)-electron bridge which is substituted with one or moreelectron donating groups.
 12. The multi-photon reactive composition ofclaim 6, wherein the photosensitizer is Rhodamine B.
 13. Themulti-photon reactive composition of claim 1, wherein the reactivespecies is selected from the group consisting of acrylates,methacrylates, styrenes, epoxies, vinyl ethers, cyanate esters, andmixtures thereof.
 14. The multi-photon reactive composition of claim 6,wherein the electron acceptor is selected from the group consisting ofiodonium salts, chloromethylated triazines, diazonium salts, sulfoniumsalts, azinium salts, triarylimidazolyl dimers, and mixtures thereof.15. The multi-photon reactive composition of claim 6, wherein theelectron donor compounds are selected from the group consisting ofamines, amides, ethers, ureas, sulfinic acids and their salts, salts offerrocyanide, ascorbic acid and its salts, dithiocarbamic acid and itssalts, salts of xanthates, salts of ethylene diamine tetraacetic acid,salts of (alkyl)_(n)(aryl)_(m)borates (n+m=4), SnR₄ compounds, whereeach R is independently chosen from among alkyl, aralkyl (particularly,benzyl), aryl, and alkaryl groups, ferrocene, and mixtures thereof. 16.The multi-photon reactive composition of claim 1, wherein the particlescomprise a metal oxide, a metal, a metal alloy, or a non-oxide ceramicmaterial.
 17. The multi-photon reactive composition of claim 16, whereinthe particles are selected from the group consisting of Al₂O₃, ZrO₂,TiO₂, ZnO, SiO₂, BaTiO₃, BaZrO₃, SrTiO₃, WO₂, WO₃, Fe₂O₃, Fe₃O₄,MnFe₂O₄, PbZr_(0.5)Ti_(0.5)O₃, BaFe₁₂O₁₉, CrO₂, Cr₂O₃, Co, MoO₂, MoO₃,SmCoO₅, and mixtures thereof.
 18. The multi-photon reactive compositionof claim 16, wherein the particles comprise metal oxide.
 19. An articlecomprising: (d) an at least partially reacted species; (b) amulti-photon photoinitiator system; and (e) a plurality of substantiallyinorganic particles, wherein the particles have an average particle sizeof less than about 10 microns in diameter, and said particles arepresent in the composition at up to about 65% by volume.
 20. The articleof claim 19, wherein the reacted species is selected from the groupconsisting of acrylates, methacrylates, styrenes, epoxies, vinyl ethers,cyanate esters, and mixtures thereof.
 21. A method for making anorganic-inorganic composite comprising: (a) providing a multi-photonreactive composition comprising: (1) a reactive species, (2) amulti-photon photoinitiator system, (3) and a plurality of substantiallyinorganic particles, wherein the particles have an average particle sizeof less than about 10 microns in diameter; (b) irradiating themulti-photon reactive composition with sufficient light to at leastpartially react the composition; and (c) removing a soluble portion ofthe multi-photon reactive composition from the resulting composite. 22.The method of claim 21, further comprising subjecting the composite to asufficiently elevated temperature for a sufficient amount of time topyrolyze the reactive species and to at least partially fuse theparticles.
 23. The method of claim 22, wherein the composite is heatedto a temperature of between about 500° C. to about 1400° C. for about 2hour to about 48 hours.
 24. The method of claim 22, wherein the dopingagent is selected from the group consisting of metal salts, fluxingagent, dyes, sol-gel precursors, organometallic precursors, andcombinations thereof.
 25. The method of claim 22, wherein the fluxingagent comprises boron oxide, boric acid, borax, and sodium phosphate.26. The method of claim 22, further comprising the step of sintering thestructure for a time and temperature sufficient to achieve asubstantially consolidated inorganic structure.
 27. The method of claim22, wherein the particles have an average particle size from about 1 nmto about 150 nm.